Constraints on extragalactic-jet characteristics from lobe observations

1986 ◽  
Vol 64 (4) ◽  
pp. 378-380 ◽  
Author(s):  
Steven R. Spangler
Keyword(s):  
Hot Spot ◽  
Radio Galaxies ◽  
Large Array ◽  
Very Large Array ◽  
Upper Limits ◽  
Measured Speed ◽  
High Mach ◽  
Jet Characteristics ◽  
Double Radio Galaxies ◽  
Spot Motion

We discuss Very Large Array spectral and polarimetric observations of the lobes of luminous, double radio galaxies. These observations can provide information on the (typically undetected) jets responsible for the sources. Spectral steepening is usually observed in the lobes, with the radio spectral index increasing with distance from the hot spot. These data can be used to infer a "speed of separation" of the hot spot and lobe material. These speeds, typically 1.0 × 104–3.0 × 104 km/s, are in agreement with hydrocode models of jets, which interpret the measured speed of separation as a combination of hot-spot motion and backflow. Polarimetric observations indicate that in at least some sources, there is an undetectably small amount of internal Faraday rotation, indicating upper limits to the thermal-plasma density of a few times 10−5 cm−3 or less. These measurements are also in agreement with the numerical beam models, provided that the beam density is substantially less than that of the background medium. We conclude that the lobe observations indicate that these sources are powered by light, high-Mach-number beams.

scholarly journals A Pilot Radio Search for Magnetic Activity in Directly Imaged Exoplanets

2021 ◽  
Vol 163 (1) ◽  
pp. 15
Author(s):  
Y. Cendes ◽  
P. K. G. Williams ◽  
E. Berger
Keyword(s):  
Pilot Study ◽  
Radio Emission ◽  
Angular Resolution ◽  
Magnetic Activity ◽  
Systematic Search ◽  
Archival Data ◽  
Large Array ◽  
Very Large Array ◽  
Upper Limits ◽  
Host Stars

Abstract We present the first systematic search for GHz frequency radio emission from directly imaged exoplanets using Very Large Array observations of sufficient angular resolution to separate the planets from their host stars. We obtained results for five systems and eight exoplanets located at ≲50 pc through new observations (Ross 458, GU Psc, and 51 Eri) and archival data (GJ 504 and HR 8799). We do not detect radio emission from any of the exoplanets, with 3σ luminosity upper limits of (0.9–23) × 1021 erg s−1. These limits are comparable to the level of radio emission detected in several ultracool dwarfs, including T dwarfs, whose masses are only a factor of two times higher than those of the directly imaged exoplanets. Despite the lack of detections in this pilot study, we highlight the need for continued GHz frequency radio observations of nearby exoplanets at μJy-level sensitivity.

scholarly journals Quasi-simultaneous radio and X-ray observations of Aql X-1 : probing low luminosities

2019 ◽  
Vol 492 (2) ◽  
pp. 2858-2871 ◽  
Author(s):  
N V Gusinskaia ◽  
J W T Hessels ◽  
N Degenaar ◽  
A T Deller ◽  
J C A Miller-Jones ◽  
...  
Keyword(s):  
Neutron Star ◽  
Large Array ◽  
Very Large Array ◽  
X Ray ◽  
Upper Limits ◽  
Order Of Magnitude ◽  
Low Mass ◽  
Low X ◽  
Power Law Index ◽  
X Ray Binaries

ABSTRACT Aql X-1 is one of the best-studied neutron star low-mass X-ray binaries. It was previously targeted using quasi-simultaneous radio and X-ray observations during at least seven different accretion outbursts. Such observations allow us to probe the interplay between accretion inflow (X-ray) and jet outflow (radio). Thus far, these combined observations have only covered one order of magnitude in radio and X-ray luminosity range; this means that any potential radio–X-ray luminosity correlation, LR ∝ LXβ, is not well constrained (β ≈ 0.4–0.9, based on various studies) or understood. Here we present quasi-simultaneous Very Large Array and Swift-XRT observations of Aql X-1’s 2016 outburst, with which we probe one order of magnitude fainter in radio and X-ray luminosity compared to previous studies (6 × 1034 erg s−1 < LX <3 × 1035 erg s−1, i.e. the intermediate to low-luminosity regime between outburst peak and quiescence). The resulting radio non-detections indicate that Aql X-1’s radio emission decays more rapidly at low X-ray luminosities than previously assumed – at least during the 2016 outburst. Assuming similar behaviour between outbursts, and combining all available data in the hard X-ray state, this can be modelled as a steep β =$1.17^{+0.30}_{-0.21}$ power-law index or as a sharp radio cut-off at LX ≲ 5 × 1035 erg s−1 (given our deep radio upper limits at X-ray luminosities below this value). We discuss these results in the context of other similar studies.

scholarly journals Optical Morphologies of Millijansky Radio Galaxies Observed by theHubble Space Telescopeand in the Very Large Array FIRST Survey

2008 ◽  
Vol 179 (2) ◽  
pp. 306-318 ◽  
Author(s):  
J. Russell ◽  
R. E. Ryan, Jr. ◽  
S. H. Cohen ◽  
R. A. Windhorst ◽  
I. Waddington
Keyword(s):  
Radio Galaxies ◽  
Large Array ◽  
Very Large Array

scholarly journals Unveiling the nature of the unidentified gamma-ray sources: blazar counterparts at low radio frequencies

2013 ◽  
Vol 9 (S304) ◽  
pp. 95-95
Author(s):  
Francesco Massaro ◽  
R. D'Abrusco ◽  
M. Giroletti ◽  
A. Paggi ◽  
N. Masetti ◽  
...  
Keyword(s):  
Radio Emission ◽  
Gamma Ray ◽  
Low Frequency ◽  
Radio Galaxies ◽  
Large Array ◽  
New Approach ◽  
Very Large Array ◽  
Very Low Frequency ◽  
Sky Survey ◽  
Order Of Magnitude

AbstractAbout one third of the gamma-ray sources detected by Fermi have still no firmly established counterpart at lower energies. Here we propose a new approach to find candidate counterparts for the unidentified gamma-ray sources (UGSs) based on the 325 MHz radio survey performed with Westerbork Synthesis Radio Telescope (WSRT) in the northern hemisphere. First we investigate the low-frequency radio properties of blazars, the largest known population of gamma-ray sources; then we search for sources with similar radio properties combining the information derived from the Westerbork Northern Sky Survey (WENSS) with those of the NRAO VLA Sky survey (NVSS). We present a list of candidate counterparts for 32 UGSs with at least one counterpart in the WENSS. We also performed an extensive research in literature to look for infrared and optical counterparts of the gamma-ray blazar candidates selected with the low-frequency radio observations to confirm their nature. On the basis of our multifrequency research we identify 23 new gamma-ray blazar candidates out of 32 UGSs investigated. I will also present the first analysis of very low frequency radio emission of blazars based on the recent Very Large Array Low-Frequency Sky Survey (VLSS) at 74 MHz. I show that blazars present radio flat spectra when evaluated at 74 MHz, about an order of magnitude in frequency lower than previous analyses. The implications of these findings in the contest of the blazars – radio galaxies connection will be discussed.

scholarly journals The faint radio source population at 15.7 GHz – IV. The dominance of core emission in faint radio galaxies

2020 ◽  
Vol 493 (2) ◽  
pp. 2841-2853
Author(s):  
I H Whittam ◽  
D A Green ◽  
M J Jarvis ◽  
J M Riley
Keyword(s):  
High Frequency ◽  
Angular Size ◽  
Radio Galaxies ◽  
Mixed Population ◽  
Source Population ◽  
Large Array ◽  
High Excitation ◽  
Complete Sample ◽  
Very Large Array ◽  
Upper Limit

ABSTRACT We present 15-GHz Karl G. Jansky Very Large Array observations of a complete sample of radio galaxies selected at 15.7 GHz from the Tenth Cambridge (10C) survey. 67 out of the 95 sources (71 per cent) are unresolved in the new observations and lower frequency radio observations, placing an upper limit on their angular size of ∼2 arcsec. Thus, compact radio galaxies, or radio galaxies with very faint jets, are the dominant population in the 10C survey. This provides support for the suggestion in our previous work that low-luminosity ($L\lt 10^{25} \, \textrm{W~Hz}^{-1}$) radio galaxies are core dominated, although higher resolution observations are required to confirm this directly. The 10C sample of compact, high-frequency selected radio galaxies is a mixture of high-excitation and low-excitation radio galaxies and displays a range of radio spectral shapes, demonstrating that they are a mixed population of objects.

Very Large Array imaging of five Fanaroff-Riley II 3CR radio galaxies

1993 ◽  
Vol 105 ◽  
pp. 1690 ◽  
Author(s):  
Ilias Fernini ◽  
Jack O. Burns ◽  
Alan H. Bridle ◽  
Rick A. Perley
Keyword(s):  
Radio Galaxies ◽  
Large Array ◽  
Very Large Array ◽  
Array Imaging

Radio hot spot in supernova remnant G109.1-1.0

1986 ◽  
Vol 64 (4) ◽  
pp. 479-481
Author(s):  
P. C. Gregory
Keyword(s):  
Supernova Remnant ◽  
Hot Spot ◽  
Time Span ◽  
Large Array ◽  
Very Large Array ◽  
X Ray ◽  
Faint Object ◽  
Sky Survey ◽  
Relationship Of ◽  
Structure Spectrum

High-resolution, very large array observations of a radio hot spot in the supernova remnant G109.1-1.0 were carried out in January 1981 and August 1984 at 6 and 20 cm to examine the possible relationship of this source to the remnant and nearby binary X-ray pulsar. The structure, spectrum, and absence of variability over a 3-year time span are consistent with a background quasar or galaxy. The source, 2258 + 586, exhibits an unresolved core that is self-absorbed at 20 cm and a one-sided jet. A very faint object appears on the red print of the Palomar sky survey, 3.7 ± 1.7 arcsec from the unresolved core.

scholarly journals Fluctuations in the Microwave Sky

1996 ◽  
Vol 168 ◽  
pp. 59-70
Author(s):  
R. B. Partridge
Keyword(s):  
Radio Emission ◽  
Large Array ◽  
Microwave Background ◽  
Very Large Array ◽  
Cosmic Background ◽  
Upper Limits ◽  
Great Progress ◽  
Sunyaev Zel'dovich Effect ◽  
Made In

This paper reviews the great progress recently made in searches for and the characterization of anisotropies in the cosmic microwave background. We now have secure detections on some angular scales and improved upper limits on others. As the sensitivity of such searches increases, understanding sources of foreground noise (e.g., Galactic and extragalactic radio emission) becomes more important. Also reviewed are the contributions aperture synthesis (interferometric) observations can make in characterizing cosmic background fluctuations and foreground sources of noise. Some recent results from the Very Large Array at λ = 3.6 cm are given; these set a limit δT/T ≲ 1.4 × 10−5on fluctuations at θ ~ 80′. Recent work on the Sunyaev-Zel'dovich effect is summarized.

scholarly journals Unveiling the cause of hybrid morphology radio sources (HyMoRS)

2019 ◽  
Vol 491 (1) ◽  
pp. 803-822 ◽  
Author(s):  
Jeremy J Harwood ◽  
Tessa Vernstrom ◽  
Andra Stroe
Keyword(s):  
Radio Galaxies ◽  
Core Region ◽  
Line Of Sight ◽  
Radio Sources ◽  
Large Array ◽  
Very Large Array ◽  
Array Configuration ◽  
The Core ◽  
Vlbi Observations ◽  
Rare Group

ABSTRACT Hybrid morphology radio sources (HyMoRS) are a rare group of radio galaxies in which differing Fanaroff & Riley morphologies (FR I/II) are observed for each of the two lobes. While they potentially provide insights into the formation of lobe structure, particle acceleration, and the FR dichotomy, previous work on HyMoRS has mainly been limited to low-resolution studies, searches for new candidates, and milliarcsecond-scale VLBI observations of the core region. In this paper, we use new multi-array configuration Very Large Array (VLA) observations between 1 and 8 GHz to determine the morphology of HyMoRS on arcsecond scales and perform the first well-resolved spectral study of these unusual sources. We find that while the apparent FR I lobe is centre brightened, this is the result of a compact acceleration region resembling a hotspot with a spectrum more consistent with an FR II (‘strong-flavour’) jet. We find that the spectra of the apparent FR I lobes are not similar to their classical counterparts and are likely the result of line-of-sight mixing of plasma across a range of spectral ages. We consider possible mechanisms that could lead to the formation of HyMoRS under such conditions, including environment asymmetry and restarted sources, concluding through the use of simple modelling that HyMoRS are the result of orientation effects on intrinsically FR II sources with lobes non-parallel to the inner jet.

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